Most of existing MAC protocol are based either on mutual exclusion (i.e. no other communication is possible within the same collision domain) or on a combination of power control and mutual exclusion. Exclusion is insured either by resource reservation (e.g. TDMA, FDMA . . . ) or with a collision management protocol (CSMA/CA). Power control improves spatial reuse and reduces interference by adapting the transmitting power of the nodes. Combining both mechanisms allows for limited amount of concurrent transmissions.
Recently, it is proven that the optimal MAC layer should not use power control but should send at full power whenever it sends. Furthermore, practical results show that it is optimal, in terms of throughput, to allow interfering sources to transmit simultaneously, and it is optimal to adapt the channel code to these interferences.
Such MAC protocol is DCCMAC (Dynamic Channel Coding—MAC), which has just appeared. According to DCCMAC, all nodes transmit concurrently at their full power. However, the interference caused by this transmission scheme of DCCMAC results in a catastrophic failure of synchronization using the conventional synchronization method since it assumes exclusion or/and power control schemes are applied. This is the first work that identifies this problem. Indeed, these finding of prior art, i.e. to transmit concurrently at the maximum power are quite recent. Further, up to the moment of writing the present document, DCCMAC is the only work that uses them and it deals only data transmission, and synchronization is out of its scope.
The document US 2004/0161064 describes an integrated circuit for processing UWB (Ultra Wide Band) IR (Impulse Radio) signal including synchronization method. The synchronization method is based on the correlation between the IR signal and the TPT (Template Pulse Train). Once the correlation output exceeds some threshold, then the signal is detected. This detection might be followed by several verification stages. The threshold is set based on equations dealing correlation output statistics.
Unlike our invention, this publication does not solve the problem of misdetection due to different power level in the signal.
The document WO 01/93444 describes methods to acquire the synchronization and for tracking based on the conventional method, i.e. a correlation is performed between the IR signal and the TPT and the detection decision is based on the correlation output. The method is described with respect to an UWB IR signal. After sweeping all search bins, the receiver locks on the bin that corresponds to the largest correlation output. This detection could be followed by several verification stages.
Unlike our invention, this publication does not solve the problem of misdetection due to different power level in the signal.
The patent U.S. Pat. No. 6,556,621 describes a synchronization method based on the conventional method. The method is described with respect to an UWB IR signal. A sweeping of search bins starts and a correlation between the TPT and the incoming UWB IR signal is performed for each bin. Sweeping search bin is done by shifting the TPT in time. A threshold check is performed on the correlation output. Once the correlation output passes this check, i.e. it is larger than the threshold, the synchronization is achieved. Supplement verification stages could be done.
Still unlike our invention, these publications does not solve the problem of misdetection due to different power level in the signal